<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Document</title>
</head>
<style>
  h1 {
    display: block;
  }
</style>

<body>
<div id="box">
  <h1>我是一张缺省图</h1>
</div>
</body>
</html>
<style></style>
<script>
  var oBox = document.getElementById("box");
  var oH = document.querySelector("h1");

  function loadImageAsync(url) {
    return new Promise((resolve, reject) => {
      var image = new Image();

      image.onload = function () {
        resolve(image);
      };

      image.onerror = function () {
        reject(new Error("Could not load image at " + url));
      };

      image.src = url;
    });
  }
  // 模拟一下异步加载图片
  // 用setTimeoutm模拟ajax调用接口，获取接口返回的图片路径，然后传入函数中，函数中已经提前创建好了
  // 图片标签。我们在.then的回调函数中自行决定插入div容器中做一些事，比如把缺省图隐藏掉
  setTimeout(() => {
    loadImageAsync(
            "https://img2020.cnblogs.com/blog/2221918/202104/2221918-20210429012928150-1671892053.png"
    ).then((res) => {
      oH.style.display = "none";
      oBox.appendChild(res);
    });
  }, 1000);
</script>
